Sorry for the delay, what items were replaced during the tune up? Do you have access to a fuel pressure tester?
Some customers may comment on rough idle after start-up, especially if the vehicle has sat overnight. These symptoms may be intermittent. The Service Engine Soon (SES) light may also be illuminated. Current misfire or history misfire codes may be detected with the Tech 2 scan tool.
A deposit build-up on the CSFI poppet valve ball and/or seat may cause the poppet ball to stick open or closed. In either case, the specific cylinder will be mis-fueled, resulting in a cylinder mis-fire condition.
A new injector unsticking and cleaning process has proven to be effective in restoring poppet valves to an "as new" condition. CSFI injector replacement should NOT be considered as a correction for this customer concern.
Check the vehicle history to determine if the vehicle is returning for a second fuel system repair for this condition. If the fuel system has been repaired for this condition previously, then inform the customer that an alternate fix is available. A new MFI fuel system has been developed that will back service the CSFI fuel system. The MFI fuel system eliminates the CSFI poppet valve ball and seat. The CSFI fuel system will need to be replaced as a unit. Refer to Central SFI to MFI Conversion instructions in this bulletin.
Notice: Individual CSFI injectors can not be replaced with MFI injectors. The entire CSFI fuel meter body will need to be replaced. The bracket used to retain the injectors in the fuel meter body is different between the CSFI and MFI unit. The unit may not seal if you mix injectors. Severe engine damage could result.
Cleaning the CSFI injectors is the preferred repair. The CSFI unit should not be replaced until cleaning has been attempted. If the vehicle should return for the same repair, then the CSFI unit can be replaced with an MFI unit. If the vehicle is out of warranty, the customer should be given the option of which fix to pursue.
Important: "GM of Canada" dealers require District Service Manager approval prior to replacing the CSFI unit with a MFI unit under warranty.
The first step of this process is to use the J 41413 Evap Pressure/Purge Station, in conjunction with the J 44466-10 pressure regulator/hose assembly, to provide the required high pressure (150 psi) source to perform the unsticking procedure. The J 39021 fuel injector tester and accessories provide the means to "energize" the injector. Some later model-year vehicles may utilize the Tech 2® to "energize" the injectors.
The second step of this process is to run the engine on a solution of 10% Top Engine Cleaner and 90% gasoline. This will effectively clean any deposits from the ball and seats of the poppets. It is very important that the engine fuel system is separated from the vehicle fuel system. Top Engine Cleaner may have detrimental effects on the fuel pump.
This procedure should be performed before any attempt to convert the fuel system to MFI.
Tighten Tighten the nuts to 3 N·m (27 lb in).
Tighten Tighten the fuel pipe bolt to 6 N·m (53 lb in).
Tighten Tighten the fuel line nuts to 30 N·m (22 lb ft).
This procedure outlines the steps required to replace the existing Central SFI Fuel System with a new MFI (Multiport Flexible Injection) Fuel System. Be sure to use the appropriate year and model Service Manual for proper disassembly and re-assembly procedure(s).
Important: Cleaning the CSFI injectors is the preferred repair. The CSFI unit should not be replaced until cleaning has been attempted. If the vehicle should return for the same repair, then the CSFI unit can be replaced with a MFI unit. If the vehicle is out of warranty, the customer should be given the option of which fix to pursue.
Notice: The number 3 Fuel Tube must be positioned behind the number 1 Fuel Tube to eliminate interference with the Upper Intake Manifold plenum when installed. See Figure 2.
Notice: Use caution when inserting injectors into lower intake manifold to be sure the correct injector is being placed into the correct hole.
Important: The Injector holes are numbered on the Lower Intake Manifold. The injectors are numbered on the side of the Fuel Meter Body.
Notice: Lack of lubrication will make installation of the Upper Intake Manifold plenum difficult and may cause damage to the O-ring.
Important: Lubricate the Fuel Inlet and Return Lines with clean engine oil before inserting them into the Fuel Meter Body.
Important: When installing fuel tubes, it is important that the tubes are oriented properly to provide minimal interference when installing the upper intake manifold plenum. Intake holes for cylinders 2, 4, 5, and 7 are closer to the fuel meter body. It is necessary to cross tube 5 over tube 7 and tube 4 over tube 2 as shown in Figure 4.
Important: Lubricate the Fuel Inlet and Return Lines with clean engine oil before inserting them in the of the Fuel Meter Body.
Cleaning Procedure Parts
Top Engine Cleaner (U.S.)
Top Engine Cleaner (Canada)
Port Fuel Injector Cleaner (U.S.)
Port Fuel Injector Cleaner (Canada)
CSFI to MFI Conversion Parts
V-6 MFI Assembly
V-6 Seal Kit
V-8 MFI Assembly
V-8 Seal Kit
56 psi is in spec. You do not have any lean fuel trim codes stored in the computer. The information you provided tells me your fuel pump is ok. The deposits on the tip if the injectors need a strong chemical and high pressure to get those deposits off. You should not run that chemical thought the fuel pump and lines. It will damage the fuel pump. The gas tank cleaners are very mild and in my experience they will not help when they get as bad as yours are. You can try it if you want, it may need to try that 2 or 3 times.
I will talk with the other drivablity tec in my shop in the AM for you. I will let him read this and see if he has any input. They can be tough when they don't set codes. Ken
I talked with the other tech in the shop today and he also was thinking injector. He thought it would be good to drive this in the A.M with a scan tool hooked up and watch the misfire counter. That will tell you if it is just one cylinder or all. Let me know how the MAF sensor did. You also might want to clean the throttle body and plate with some carb cleaner and a rag. Rub the plate and bore until they are shinny. Hole your foot down on the gas until it starts and then let off. If you have deposits built up in throttle body, the motor may not be getting enough air on take off. The motor uses more fuel and air when cold. You may also want to hook up a fuel gage and see if the fuel pressure holds after you turn off the motor. The fuel pressure regulators are known for dripping fuel when they first start going out. Ken